The WHO today warned of a virulent new virus affecting vulnerable groups in the Mid‐West and Eastern USA. The outbreak, which began in the Mid‐West’s extensive Great Lakes “Freshwater” river system, has recently jumped the “Saltwater” barrier, meaning that the entire population of its target species—“Mainstream” economists—is now at risk.

Speaking on behalf of the WHO, Dr Cahuc explained that the virus works by turning off the one genetic marker that distinguishes this species from the rest of its genus, the Human Race. This is the so‐called “Milton” gene (Friedman, 1953), which goes dormant in other Humans as they pass through puberty. Its inactivity reduces their imaginative capacity, making it impossible for them to continue believing in such endearing infantile fantasies as the Tooth Fairy and Santa Claus. While regrettable, this drop in imagination is necessary to prepare Humans for the adult phase of their existence.

“Professor Milton Friedman found a way to re‐activate this gene during PhD training, using his ‘as if’ gene splicing technique”, Dr Zylberberg elaborated. “This enabled a wonderful outpouring of imaginative beliefs by Mainstream Economists, which gave birth to concepts like NAIRU, Money Neutrality, Rational Expectations, and eventually even DSGE models. This wealth of imagination was regarded by Mainstream Economists as a more than sufficient compensation for returning to the child‐like phase of the Human species.”

Looking at what famous mainstream economists — like e.g. Paul Samuelson and Gerard Debreu — have come up with, there is no indication at all they produce rigorous and successful explanations or predictions of real-world phenomena. In physics, it’s all different. There one has often been able to, by the use of mathematics, to produce both rigorous and successful explanations and predictions. But then, of course, the material world is something quite different from the social world …

Mainstream economic theory today is still in the story-telling business whereby economic theorists create mathematical make-believe analogue models of the target system – usually conceived as the real economic system. This mathematical modelling activity is considered useful and essential. Since fully-fledged experiments on a societal scale, as a rule, are prohibitively expensive, ethically indefensible or unmanageable, economic theorists have to substitute experimenting with something else. To understand and explain relations between different entities in the real economy the predominant strategy is to build mathematical models and make things happen in these ‘analogue-economy models’ rather than engineering things happening in real economies.

Formalistic mathematical-deductive ‘Glasperlenspiel’ can be very impressive and seductive. But in the realm of science, it ought to be considered of little or no value to simply make claims about the model and lose sight of reality.

Mainstream economists love to depict heterodox economists’ views on the use of mathematics as coming from sadly misinformed and misguided people who dislike and do not understand much of it. This is really a gross misapprehension. We do not misunderstand the crucial issues at stake — and many of us have spent decades on using mathematics and statistics in our research and teaching. To be careful and cautious is not the same as to dislike. Quite the contrary. We know the crucial issues all too well — and are not satisfied with the validity and philosophical underpinning of the assumptions made for applying mathematical methods in economics.

Without strong evidence, all kinds of absurd claims and nonsense may pretend to be science. Let us not forget what Paul Romer — someone I guess not even the most outré mainstreamer would call a heterodox economist — said in his masterful attack on ‘post-real’ economics a couple of years ago:

Math cannot establish the truth value of a fact. Never has. Never will.

We have to demand more of a justification than rather watered-down versions of ‘anything goes’ when it comes to the main postulates on which mainstream economics is founded. If one proposes ‘efficient markets’ or ‘rational expectations’ one also has to support their underlying assumptions. As a rule, none is given, which makes it rather puzzling how things like ‘efficient markets’ and ‘rational expectations’ have become the standard modelling assumption made in much of modern macroeconomics. The reason for this sad state of ‘modern’ economics is that economists often mistake mathematical beauty for truth.

So — let’s hope the reality virus will keep on infecting mainstream economics!